Search results for "mixture"
showing 10 items of 1178 documents
Influence of the presence of surfactants and humic acid in waters on the indophenol-type reaction method for ammonium determination.
2005
Abstract This work has evaluated the influence of humic acid and/or surfactants in the quantification of ammonium in waters with the indophenol-type reaction method. Thymol has been employed with the colorimetric method for sample ammonium concentrations between 0.25 and 1 mg L −1 . In addition, SPE/diffuse reflectance method has been used for quantification of ammonium at low concentrations (between 0.025 and 0.25 mg L −1 ). Matrix effect owing to humic substances were observed with the colorimetric method when the concentration was equal or higher than 25 mg L −1 . Lower concentrations of humic compounds produced matrix effects with the more sensitive SPE/diffuse reflectance method. Gener…
Transformation of Iodide in Natural and Wastewater Systems by Fixation on Humic Substances
2000
Separation of different fractions of humic substances (HS) by their molecular weight was carried out by size exclusion chromatography (SEC). The fixation of inorganic iodide by HS of these fraction...
Structurally bound lipids in peat humic acids
2001
Humic acids from highly decomposed peat were subjected to oxidation with alkaline cupric oxide (CuO) at 170°C (single oxidation). Oxidation products were isolated as three fractions, oxidized humic acids, fulvic acids and lipophilic compounds. Isolated oxidized humic acids were subsequently re-oxidized (sequential oxidation) under the same conditions, and released lipophilic compounds were isolated. Lipids released during single and sequential oxidations were determined using capillary gas chromatography and mass spectrometry. Identified compounds accounted for 3.3 and 0.12 wt.% of humic acid content, respectively. Lipid profiles of lipophilic fractions released during single and sequential…
Enzymatic and Chemo-Enzymatic Approaches Towards Natural and Non-Natural Alkaloids: Indoles, Isoquinolines, and Others
2010
Abstract The multi-step enzyme catalysed biosyntheses of monoterpenoid indole and isoquinoline alkaloids are described. Special emphasis is placed on those pathways leading to alkaloids of pharmacological and medicinal significance which have been fully elucidated at the enzyme level. The successful identification and cloning of cDNAs of single enzymes and their application provides great opportunities to develop novel strategies for both in vitro and in vivo alkaloid production in whole plants or tissue cultures, as well as in microbial systems such as Escherichia coli and yeast. Enzyme crystallisation, 3D analyses and site-directed mutation allowed rational engineering of enzyme substrate…
Effects of compost input and tillage intensity on soil microbial biomass and activity under Mediterranean conditions
2010
Organic amendment and tillage reduction are two common practices to contrast soil organic matter decline, thus promoting sustainable cropping and carbon sequestration. In a horticultural land use system under Mediterranean climate, we evaluated the 9-year effects of two compost inputs (15 and 30 t ha−1 y−1, low and high input, respectively) and two tillage intensities (intensive and reduced) on soil macronutrients concentration, microbial biomass and activity. Total organic C, total N and POlsen were smaller in plots amended at low input, whilst intensive tillage decreased them at both compost inputs. These decreases in intensively tilled plots was ascribed to the disruption of soil aggrega…
Effective pair potential between charged nanoparticles at high volume fractions
2017
Simulations of charged colloidal dispersions are technically challenging. One possible workaround consists in reducing the system to the colloids only, whose interactions are described through an effective pair potential, wf. Still, the determination of wf is difficult mainly because it depends on the colloidal density, ϕ. Here we propose to calculate wf from simulations of a pair of colloids placed in a cubic box with periodic boundary conditions. The variation in ϕ is mimicked by an appropriate change in the concentration of counterions neutralized by an homogeneous background charge. The method is tested at the level of the primitive model. A good description of the structure of the coll…
On the regioselectivity of the Friedländer reaction leading to huprines: stereospecific acid-promoted isomerization of syn-huprines to their anti-reg…
2001
Abstract Racemic 12-amino-6,7,8,11-tetrahydro-7,11-methanocycloocta[ b ]quinoline derivatives ( syn -huprines) substituted at the 9-position with a methyl or ethyl group, and both enantioenriched forms of the 9-ethyl derivative, obtained by chiral MPLC resolution of the racemic mixture, were readily converted to the corresponding anti -isomers (huprines) by stereospecific acid-promoted (AlCl 3 or triflic acid) isomerization of the endocyclic CC double bond from the 9(10)- to the 8(9)-position. These results support the hypothesis that the hitherto unseen syn -huprines are also formed under the usual acidic Friedlander reaction conditions used to prepare the known huprines, but rearrange in…
Interaction Mechanisms between guaiacols and lignin: the conjugated double bond makes the difference.
2011
Lignin is considered to be responsible for a selective sorption of phenolic compounds on wood. In order to investigate the mechanisms involved, two similar guaiacol compounds--only differing by the nature of the para side chain--were adsorbed on oak wood extracted lignin. Vapor sorption-desorption isotherms indicated that about 3.5 wt % of 4-vinylguaiacol is adsorbed near saturation whereas it is only 0.8% for 4-ethylguaiacol. For both compounds, the isotherms displayed a hysteresis though significantly greater for 4-vinylguaiacol. Analyses of the hydroxyl stretching region of FTIR spectra of the lignin/4-ethylguaiacol and lignin/4-vinylguaiacol complexes indicated that physisorption via hy…
Performance-based characterization of recycled polymer modified asphalt mixture
2021
Due to the introduction of secondary materials, the asphalt mixtures to be designed and tested in our laboratories are constantly becoming much more complex than traditional asphalt mixtures making difficult to use conventional laboratory procedure and/or predict expected results. This study proposes a comprehensive characterization of asphalt mixture modified with recycled polymer compound by using both wet and dry process proposing adjustments to laboratory mixing and sample compaction procedure. Accordingly, three AC20 Hot Asphalt Mixture (HMA) were designed and their conventional and performance related properties were assessed by looking at a) Indirect Tensile test (ITS) a) moisture da…
Effect of storage and composting on the properties and degradability of cattle manure
1995
Abstract Stockpiling or thermophilic composting of cattle manure resulted in significant carbon losses of 17% and 26.4% and relative nitrogen gains of 25% and 32.7% for stockpiled and composted manure, respectively. As a consequence, C/N ratios decreased with increasing time of storage or composting. However, neither the pH nor the mineral nitrogen and organic carbon contents of the 0–50 μm fractions were significant indicators of the transformations of these materials. The degradability of the manure was measured by incubation for 2 weeks in a brown calcareous soil, following 1 week of preincubation. The biodegradation index (BI) or the proportion of CO 2 released from the amended soil in …